There are a number of factors to be considered in the formulation of a foam control material for use in controlling foam in pulp mill and paper mill operations and other operations, to eliminate or minimize the interference of foam in the particular operation. A foam control material should have the ability to decrease an already-formed foam to a low level in a short period of time and, additionally, the ability to prevent the formation of foam from the liquor once the material is present, over an extended period of time.
Foaming occurs in pulp and paper mills at a number of locations and many formulations have been suggested to control such foam, with the individual formulations being constructed for the particular location. Such locations include the brown stock washer wherein hot pulp is washed to remove entrained pulping liquor, the screen room wherein the washed pulp from the brown stock washer is subjected to displacement washing and cooling prior to passage to the bleach plant, and the paper making machine wherein the bleached pulp is formed into paper. In the first two locations, foaming occurs in alkaline medium, while, in the latter case, foaming occurs in an acid or neutral medium.
Almost universally the defoamer compositions have been provided in dispersed or dissolved form in an organic liquid carrier, typically a hydrocarbon oil, the carrier generally constituting in excess of 90% of the total composition. The use of such oils has been a convenient manner of application of the active defoaming chemicals but the presence of such oils in pulp mills has considerable drawbacks, including the formation of deposited pitch and water pollution. Additionally, the high proportion of carrier in the composition leads to the transportation of large volumes of defoamer product.
There has, therefore, long been sought a defoamer composition dispersible in water in place of mineral oil and which gives competitive performance characteristics. The present invention provides a water-dispersible defoamer composition which, in use, is substantially oil-free.